Process for the introduction of graphitic carbon into light metals or light metal alloys



- Patented Aug. 22, 1939 PATENT 1 OFFICE rnoeuss ron THE. INTRODUCTIONor GRAPHITIO cannom'm'ro LIGHT METALS on mcn'r METAL ALLOYS HeinrichBorofski, Frankfort-on-the-Main, Germany, assignor of one-half to thefirm Mettmanner Britannia-Wareni'abrik W.

Seibel,

Mettmann, Rhineland, Germany No Drawing. Application December 30, 1937,Se-' rial No. 182,544. In Germany January 9, 1936 16 Claims. (01.75-435) This invention relates to a new or improved process'for theintroduction of graphitic carbon into light metals or light metalalloys. It is already known that an addition of carbon in the 5 form ofgraphite, is advantageous, particularly in reducing the co-eflicient offriction. This socalled graphiting of metals or alloys was previouslyeffected by introducing graphite powder into the melt. When thesegraphited metals or alloys 10 are in their melted'condition, there is atendency for separation to take place on account of the great differencebetween the 'speciflc weight of the graphite and that of the metal. Topre vent this separation, it has already been proposed 15 to weight thegraphite to be introduced into the metal in order to make its specificweight equal to or approximately equal to that of the metal. Attemptshave been made to bring about the weighting by galvanically coating thegraphite 20 particles with a coating of metal of higher specific weight,for instance of copper or nickel, or by incorporating the graphite inametal or alloy, and

by then introducing the galvanically coatedgraphite particles or themixture of graphite and 25 metal into the alloy to be graphited. Theseattempts, however, have had no success, because,

on the one hand, it is diflicult to provide'a metal coating upongraphite, which travels in the galvanic bath from. the cathode to theanode, and,

30 on the other hand, the affinity of the coating and weighting metalsto the metal to be graphited or to the alloy to be graphited is ofconsiderableimportance, and frequently makes the weighting of thegraphite inoperative by alloying the as weighting metal with the metaltobe graphited.

' Finally, especially with light metals or light metal alloys which areparticularly subject to oxidation it is necessary that in the graphitingno mois ture of any kind should be brought into the fluid metal, sincethereby the formation of oxide and.

in certain circumstances, even the formation of carbides, occurs, andthis would make the graphited alloys 'llnserviceable, by reason ofithe'great hardness of the oxides and carbides, f r the very "purposes inwhich good ability to s de is concemed. n coating the graphite particleswith galvanic metal coatings, fluid occlusions cannot, however. beavoided with certainty.

' The invention concerns a process for the pro- 50 duction of colloidmixtures from light metals or ,lightmetal alloys and carbon especiallyin the form of graphite, in which the disadvantages of thepreviouslyknown processes are avoided by for weighting the graphite, notpure metals metal compounds, for instance metallic salts, which aredecomposed before or dur-' ing graphiting, for example by change oftemperature or by chemical reaction, whereby the metal is liberated andthe individual graphite particles are weighted. The process may, withadvantage, be carried out by stirringup with the I graphite a metalcompound dissolved in water or other fluid, until the graphite particlesare completely moistened or penetrated by thesolution and freed from theadhering air, and then removing the fluid, for instance by filtering andevaporation, and introducing the residue into the metal to be graphited.I

If, for instance, an aluminium alloy is to be graphited, there is usedas a weighting medium for the graphite lead acetate Pb(CzH:iOz) 2.31120,for instance, which is completely dissolved in any suitable solvent, forinstance, water. The graphite is mixed into this solution and is thenfreed from adhering air by lengthy stirring and kneading and completelymoistened and penetrated by the solution. The mixture of dissolved leadacetate and graphite is preferably left standing for some time and isthen again stirred or kneaded. The fluid is now evaporated attemperatures of about 100 C. and thereby the water of crystallisation ofthe lead acetate is also removed and the mass obtained introduced intothe fluid aluminium alloy. Even at temperatures below 200" C. the leadacetate decomposes. Al-

though acetone and carbonic acid escape, the lead and carbon do notvaporise at the temperatures employed and therefore remain in the andweight the graphite. The weighted graphite permeates the alloy to be phted inthe flnest distribution and forms a very stable colloidal mixturewith the alloy. An aluminium alloy graphited in this manner w' anextraordinarily low frictional coemcient which equalsandevenbettersthatofthebestwhitebearing 4o metals.

The invention extends, of course not to I the graphiting of aluminiumalloys by weighting .the graphite with the aid ,of lead acetate, leadchloride or any other lead compound, but is also applicable withadvantage to the graphiting of other metals and alloys and employingcompounds of other metal as the media for the graphite. In the exampledescribed above,

alead compoundhasbeenselectedasweightingso the main components easilycombine with lead.

It may be presumed that on mixing the graphite with the lead compound, acomplete penetration of the graphite occurs, and thus the air or anyother gas adhering or tending to adhere to the graphite particles is.displaced, so that the buoyancy of the graphite in the melt isdecreased, and the weighting medium is in no case completely dissolvedout of the graphite particles.

The metal compounds to be employed for weighting the graphite can be sochosen that either one only or several components thereof remain in thealloy to be graphited. When lead acetate is used, carbon also remains inaddition to lead in the alloy to be graphited. If required, compoundscontaining carbon may be added alone to the metal or alloy as theweighting medium, for instance lead acetate by itself without anadmixture of graphite, in as far as, during the process, a decompositionof the weighting medium occurs or can be'readily caused to occur.Finally, instead of solutions of metal compounds, there may also be usedas weighting media suitable mixtures of lead or other metals or alloysand graphite, provided that all the materials are reduced to colloidfineness.

What I claim is:

1. Process for graphiting light metals which comprises mixing graphiticcarbon with a decomposable metal compound, introducing such mixture intoa melt of said light metal and bringing about decomposition of saidmetal compound with liberation of metal in close association with saidcarbon.

2. Process for graphiting light metals which comprises mixing graphiticcarbon with a carbon containing heavy metal compound decomposable tometal and carbon at the melting point of said light metal, andincorporating the mixture in a melt of said light metal.

3. Process for graphitlng light metals which comprises introducing intoa melt of said light metal a carbon-containing metal compound adapted atthe temperature of the melt to be decomposed into metal and carbon andbringing about solidification of the light metal without segregation ofsuch carbon.

4. Process for graphiting light metal which comprises introducing into amelt of said light metal a mixture of graphitic carbon and a metallicsalt selected from the group of metallic salts which under the influenceof heat liberate metal adapted to associate with graphite particles, andbringing about solidification of the light metal without substantialsegregation of car- 5. Process as claimed in claim 2 in which the heavymetal compound is an acetate.

6. Process for graphiting light metals which comprises moistening andimpregnating graphitic carbon with a solution of a lead salt, expellingair and solvent, incorporating the graphitic carbon so treated in a meltof light metal and solidmetal graphitic carbon and a metallic saltselected from the group of metallic salts which under the influence ofchemical substances liberate metal adapted to associate with graphiteparticles, and bringing about solidification of the light metal withoutsubstantial segregation of carbon.

9. The process for graphiting light metals or alloys thereof, whichconsists in producing a mixture of graphitic carbonwith a metal compoundwhich decomposes at the melting temperature of the light metal or alloyto be graphited, introducing said mixture into the molten light metal oralloy, and bringing about solidification of such metal or alloy.

10. Process as claimed in claim 9, in which the mixture of graphiticcarbon and decomposable metal compound is in a dry condition at the timeof its addition to the molten light metal or alloy.

11. Process as claimed in claim 9, in which a compound of a heavy metalis used as the decomposable metal compound.

12. Process as claimed in claim 9, in which a lead compound is used asthe decomposable metal compound.

13. Process according to claim 1, in which a lead compound is used asthe decomposable metal compound.

14. Process according to claim 1, in which lead acetate is used as thedecomposable metal compound.

15. The process for graphiting light metals or alloys thereof, whichconsists in mixing graphitic carbon with a solution of a metal compoundwhich decomposes at the melting temperature of the light metal or alloyto be graphited,

removing air and the solvent from said mixture of graphitic carbon andmetal compound, introducing the resulting dry mixture into the moltenlight metal or alloy, and bringing about solidification of such metal oralloy.

16. The process for graphiting light metals or alloys thereof, whichconsists in mixing graphitic carbon with a solution of a decomposablemetal compound, removing air and the solvent from said mixture ofgraphitic carbon and metal compound, introducing the resulting drymixture into the molten light metal or alloy, and bringing aboutsolidification of such metal or alloy.

HEINRICH BOROFSKI.

